I use a content tag that brings a graphic element.

        <xsl:if test="tags/BLOCKINGNEWS and $rendering-context='back'">
            <img src="{ametys:skinURL('img/alerte-bloquante.png')}" alt="bloquante" class="alert-blocker" />
        </xsl:if>

After the closing / opening of the page, restart the application, reset the application it is not taken into account.
I must edit and save the content to display the pictogram.

The manipulation is long to describe, see the video: http://people.anyware-services.com/~lperier/CG26/BugAlerte.ogv